Just below a proof summary you may see a message such as the following.

TIME-TRACKER-NOTE [:TAU]: For the proof above, the total runtime spent
in the tau system was 30.01 seconds. See :DOC time-tracker-tau.

Both of these messages are intended to let you know that certain prover
heuristics (see tau-system) may be slowing proofs down more than they are
helping. If you are satisfied with the prover's performance, you may ignore
these messages or even turn them off by disabling time-tracking
entirely (see time-tracker). Otherwise, here are some actions that you can
take to solve such a performance problem.

The simplest solution is to disable the tau-system, in either of the
following equivalent ways.

But if you want to leave the tau-system enabled, you could investigate the
possibility is that the tau-system is causing an expensive
:logic-mode function to be executed. You can diagnose that problem
by observing the rewriter -- see dmr -- or by interrupting the system
and getting a backtrace (see set-debugger-enable). A solution in that case
is to disable the executable-counterpart of that function, for example in
either of these equivalent ways.

As a result, the tau-system will be weakened, but perhaps only negligibly.

In either case above, you may prefer to provide :in-theory hints
rather than :in-theoryevents; see hints.

A more sophisticated solution is to record values of the
:logic-mode function in question, so that the tau-system will look
up the necessary values rather than calling the function, whether or not the
executable-counterpart of that function is enabled. Here is an example of a
lemma that can provide such a solution. See tau-system.